The present invention relates to motor driving circuits, which are suitable for use in optical disk apparatus, for example.
Conventionally, use has been widely made of a H-bridge circuit to constitute a circuit for driving a loading motor which serves to open/close a tray of an optical disk apparatus.
As is known, an optical apparatus has a tray for carrying thereon an optical disk, which is designed to be capable of closing by hand power of an operator even when the whole of the apparatus is in an off-state. A loading motor for opening/closing the tray is then actuated to perform a rotation operation for the opening/closure of the tray. At this time, the loading motor is to act as a generator to generate a counter electromotive force across the terminals of the motor. If this electromotive force is too large, it will lead to a problem such that the peripheral circuits may suffer malfunctions or failures.
To cope with such a problem, JP-A-2003-199392 discloses measures in which an overvoltage detecting circuit is provided for detecting that an H-bridge circuit constituting a loading motor driving circuit has at its output end a voltage higher than a power source voltage by a predetermined value or a voltage lower than a ground voltage by a predetermined value, so that an output transistor arranged on the ground side and connected to an output end of the H-bridge circuit at a voltage higher than the power source voltage by a predetermined value or an output transistor arranged on the power source side and connected to an output end of the H-bridge circuit at a voltage lower than the ground voltage by a predetermined value is turned on by an output of the overvoltage detecting circuit.